A combination of a television (TV) receiver and a video cassette recorder (VCR) provides a consumer with a useful combination of functions in a single piece of electronic equipment. Using a TV/VCR combination, a viewer can watch a television program from either a pre-recorded video cassette tape, or from a broadcast or cable station. In addition, a viewer may record a received broadcast or cable television program on a video cassette tape.
Current TV/VCRs have simply combined the circuitry found in a VCR with that found in a TV receiver. For example, in an NTSC TV receiver, there is a chrominance signal processor for processing the quadrature modulated chrominance component, modulated on a 3.58 MHz color subcarrier, in the received composite television signal. This chrominance signal processor includes a quadrature demodulator having a pair of in-phase and quadrature mixers responsive to the chrominance signal and to a pair of in-phase and quadrature demodulating carrier signals. The carrier signals are produced by a crystal oscillator operating at 3.58 MHz and phase controlled by the color burst signal. The signals from the pair of mixers is then processed by a corresponding pair of low pass filters (LPFs). The output signals from the LPFs are respective color difference signals R-Y and B-Y. A phase locked loop, responsive to the color burst signal, controls the phase of the pair of quadrature demodulating carrier signals.
In a VHS VCR, however, the color-under signal, when recorded and played-back, is modulated on a line-locked 629 kHz carrier signal whose phase is varied by 90 degrees from line to line, called a 4-phase carrier signal in the remainder of this description. During playback, this color-under signal is never demodulated in the VCR. Instead, the VCR contains an up-converter, for changing the center frequency of this 629 kHz color-under signal to 3.58 MHz, to produce an NTSC TV-type chrominance signal. This chrominance signal is then combined with the played-back luminance signal to form an NTSC composite video signal which can be processed by a standard TV receiver as described above.
In present TV/VCRs, the VCR section contains essentially the same circuitry as in a standalone VCR, and the TV section contains essentially the same circuitry as a standalone TV, including the color-under and chrominance circuits described above. The redundant chrominance processing circuitry in current TV/VCRs leads to increased costs to manufacture due to the cost of the redundant parts and the added manufacturing steps necessary to fabricate and install the redundant parts. In addition, reliability of current TV/VCRs is reduced due to the possibility of failure of the redundant parts. A TV/VCR which eliminates the need for redundant parts is desirable to lower cost and increase reliability.